The present invention is directed to the art of fabricating heat exchanger tubes or conduits that are provided with twisted tapes for promoting turbulent flow within the tubes for enhancing heat exchange properties and, more particularly, to a method for brazing the twisted tapes to the walls of the tubes for increasing the heat transfer from the fluid within the tubes to the tube walls.
Heat exchangers are conventionally fabricated by positioning a plurality of tubes within a housing and then passing a fluid through the tubes to effect heat transfer from the fluid within the tubes to a fluid medium surrounding the tubes or the converse thereof.
The efficiency of the heat exchangers has been significantly increased by generating turbulent flow within the heat-exchanger tubes for enhancing the heat transfer from the fluid within the tubes to the tube walls. This turbulent flow is provided by inserting convoluted or twisted tapes in the passageways within the tubes. The heat transfer between the fluid within the tubes and the tube walls is also provided by conduction through the twisted tapes to the tube walls. To provide this conductive heat transfer the edges of the twisted tapes are joined to the inner walls of the tubes by brazing or the like.
By practicing known techniques for brazing the twisted tapes to the inner walls of the tubes, folds and powder of the filler metal are placed at various locations along the tube so that only spot brazing occurs over the length of the tape within the tube. Thus, any increase in heat transfer by conduction is somewhat minimal in that insufficient contact is established between the twisted tape and the tube wall to provide the desired extent of heat transfer.